How to upgrade modem firmware of a jailbreaked iPhone?

Hai friends!

I am an unlocker (beginner) i have iPhone 4 which is jailbreaked and cydia installed through PANGU. When i try to run ultrasnow, it shows me the following error. Please help me. i am desperately in need of this.

Current version details:
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Version: 7.1.2 (11D257)
Model: MD198B/A
Modem Firmware: 04.12.09

Cydia error details:
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(Error message: The requested modifications cannot be applied due to required dependencies or conflicts that cannot be automatically found or fixed)

mobilesubstrate>=0.9.3209- 1
iOS Firmware <5.0
mobilesubstrate>=0.9.3900

If my understanding is correct, i have to upgrade my modem firmware to 5.0 and above. Please help me, how to do this!

Regards,
Frank